Multi-State Tax Filing for Startups: Nexus, Registration, and Apportionment Basics

Income tax nexus is the connection between a business and a state that lets the state tax the business's income. Unlike sales tax nexus, which now turns mostly on sales volume, income tax nexus has traditionally been triggered by physical presence: an employee, office or property in the state.

Remote work has expanded that exposure. A Delaware C corporation headquartered in San Francisco with remote employees in New York, Texas and Colorado will typically have nexus in California, New York and Colorado. Texas has no corporate income tax but imposes a franchise tax, covered below.

Some states also apply economic nexus to income tax. The Multistate Tax Commission's model "factor presence" standard uses $500,000 of sales, $50,000 of property, $50,000 of payroll, or 25% of total sales, property or payroll in the state. California and New York are among the states with their own economic nexus thresholds, and those thresholds are adjusted over time, so check the current figure for each state.

The practical rule: every state where you have an employee likely creates a filing obligation. Track where team members physically work, including remote employees, and review the filing requirements in each of those states.

Once you have nexus in a state, you generally register with its tax authority and file annual returns. Registration usually involves qualifying as a foreign corporation with the Secretary of State (if you were formed elsewhere), getting a state tax account, and setting up access to the state's online portal.

Common state corporate returns include California Form 100, New York Form CT-3 and Illinois Form IL-1120. Each state has its own form, due date and extension rules.

Many states also require an annual report with the Secretary of State, separate from the tax return, with its own fee. California's Statement of Information costs $25. Delaware corporations pay a $50 annual report fee plus franchise tax, which has a minimum of $175 under the Authorized Shares Method or $400 under the Assumed Par Value Capital Method, due March 1.

Pass-through entities (S corporations and LLCs) often have more work: some states require composite returns on behalf of nonresident owners, and others require withholding on nonresident owners' shares. Rules differ state by state.

When a company has nexus in several states, each state can tax only the share of income attributable to it. Apportionment formulas set that share.

Historically most states used an equally weighted three-factor formula: (state sales ÷ total sales + state property ÷ total property + state payroll ÷ total payroll) ÷ 3. Over the past two decades most states have moved to a single sales factor or a formula that heavily weights sales. California, New York, Illinois and Pennsylvania use single-sales-factor apportionment, and the Texas franchise tax apportions by gross receipts.

For SaaS companies, sourcing is the key question: which state is a sale "in"? California uses market-based sourcing under Revenue and Taxation Code §25136, assigning service revenue to where the customer receives the benefit, which for SaaS is generally the customer's location. A few states still use cost-of-performance rules that look at where your employees do the work. The sourcing method can change your apportionment percentage substantially.

For example, a California-based SaaS company that sells nationally, with 15% of its revenue from California customers, apportions about 15% of its income to California under single-sales-factor market-based sourcing, even if every employee is in California.

Single-sales-factor apportionment multiplies total taxable income by the share of sales sourced to each state. The arithmetic is easy; the real work is sourcing each sale correctly.

Example (hypothetical figures): a Delaware C corporation with $2,000,000 of federal taxable income, before state modifications, has nexus in California, New York and Colorado. Under market-based sourcing, 20% of its receipts come from California customers, 10% from New York customers and 5% from Colorado customers. The other 65% comes from states where it has no nexus.

• California: $2,000,000 × 20% = $400,000 apportioned. At California's 8.84% corporate rate, that is $35,360 of tax before credits.
• New York: $2,000,000 × 10% = $200,000 apportioned and taxed under New York's own rate schedule.
• Colorado: $2,000,000 × 5% = $100,000 apportioned to Colorado.

Only 35% of the company's income is taxed by any state here. Income assigned to states where you lack nexus is sometimes called nowhere income, and some states use throwback or throwout rules that pull those sales back into the numerator or drop them from the denominator. Check each state's rule before counting on the gap.

Most venture-backed startups have losses in the early years, not taxable income. They still file in each nexus state, because the return establishes the state net operating loss carryforward and many states charge a minimum tax regardless of income. California's minimum franchise tax is $800, although a newly formed or qualified corporation is exempt in its first taxable year.

Three state-specific issues come up repeatedly.

Texas franchise tax. Texas taxes margin, computed as the lesser of total revenue minus cost of goods sold, total revenue minus compensation, 70% of total revenue, or total revenue minus $1 million. The rate is 0.75% for most businesses and 0.375% for retail and wholesale. For reports due in 2026 and 2027, entities with total revenue of $2,650,000 or less owe no tax (the threshold was $2,470,000 for 2024 and 2025), but they still file a Public Information Report or Ownership Information Report. Reports are due May 15.

Pass-through entity (PTE) tax elections. Most states with an income tax now let partnerships and S corporations elect to pay state tax at the entity level, with owners getting a credit on their personal returns. The election moves the state tax deduction from the individual return, where the federal SALT deduction is capped, to the entity return, where it is not. The cap dates from the 2017 Tax Cuts and Jobs Act and was raised, not removed, by the One Big Beautiful Bill Act (P.L. 119-21), so the election still has value for many owners. California and New York both offer one. This matters only for S corporations and LLCs; a venture-backed C corporation does not benefit.

Voluntary disclosure. If you have had nexus in a state for years without filing, most states offer voluntary disclosure agreements that reduce penalties and often limit the lookback period. Coming forward is generally a better outcome than being found in an audit or through a payroll registration.

Multi-state compliance needs a system, not heroics. A workable setup has four parts.

1. A nexus study, updated at least annually. Document where you have employees, offices and equipment, where you cross economic thresholds, and what you must file in each state. Update it whenever you hire in a new state or open an office.
2. A compliance calendar. State due dates vary, and not every state follows the federal extension automatically. Late filing penalties apply in most states, so track every deadline.
3. A preparer with multi-state experience. State returns require apportionment, state modifications to federal taxable income (many states have not conformed to every federal change, including parts of the 2025 federal law), and state credits.
4. Periodic entity review. As your footprint grows, intercompany agreements or state-specific elections may make sense, but they need to be implemented carefully to hold up on audit.

We handle nexus analysis, state registrations, multi-state return preparation and monitoring of state law changes for startups. The figures here were checked in October 2026; this is general information, not tax advice for your specific facts.